The present invention relates to an engine starter motor and, particularly, to an engine starter motor having a water proof structure.
An engine starter motor of the so-called overhang type is known and an example is disclosed in Japanese Kokai (Utility Model) No. 61-6679. The construction of this known engine starter motor will be described with reference to FIGS. 7 and 8.
The engine starter motor shown in FIGS. 7 and 8 has a front frame portion 1 of a frame structure. The front frame portion 1 is formed with an opening 2 through which an extension 3 of an armature shaft of a d.c. motor (not shown) provided in the frame extends forwardly. A pinion slider 4 is slidably and rotatably mounted on the extension 3 through a bearing 5. The pinion slider 4 is supported slidably and rotatably by a bearing 6 arranged inside the front frame portion and thus the extension 3 is also supported thereby.
In such starter motor structure, the pinion slider 4 has a forward end portion formed with a pinion 4a therearound and a rear end forming a clutch-inner 7a which is a constitutional component of an over-running clutch 7 having a clutch-outer 7b and rollers 7c for transmitting rotation of the clutch-outer to the clutch-inner. An intermediate portion of the pinion slider between the pinion 4a and the clutch inner 7a provides a sliding support surface 4b to be supported by the bearing 6.
Reference numerals 8, 9, 10 and 11 in FIGS. 7 and 8 depict an oil seal, a dust-proof cap mounted detachably on the front end portion of the pinion slider 4, a stopper mounted on the front end of the extension 3 for preventing the pinion slider 4 from dropping out and a ring gear of an engine, respectively.
An operation of this construction will be described briefly.
When the over-running clutch 7 is moved forwardly along an arrow 12 by means of a shift lever (not shown), the pinion slider 4 slides on the extension 3 integrally, so that the pinion 4a goes out from the opening 2 of the front frame 1 and meshes with the ring gear 11 as shown in FIG. 8.
Immediately before the pinion 4a meshes with the ring gear 11, power is supplied to the d.c. motor and rotation of its armature shaft is transmitted from the clutch-outer 7b of the over-running clutch 7 through the rollers 7c to the clutch-inner 7a and then the pinion slider 4. Thus, at the time of meshing, the engine is started through the ring gear 11.
When the pinion slider 4 is rotated by the engine at high speed after the engine is started and before the pinion slider is retracted, the clutch-inner 7a rotates at higher speed than the clutch-outer 7b. Therefore, the rollers 7c which serve as a one-way clutch are separated from the clutch-inner and the clutch-outer to allow the clutch-inner 7a to rotate freely to thereby prevent a transmission high speed rotation of the pinion slider to the engine.
The oil seal 8 is shown in FIG. 9. The oil seal 8 is constituted by a an steel ring 8a having an L shape cross section and a rubber ring 8b having a V shape cross section and fitted onto an inside of the steel ring 8a. The steel ring 8a is pressure-fitted on a shoulder portion 1a of the front frame portion 1 with a space with respect to the bearing 6 and a lip portion 8c of the rubber ring 8b is in resilient contact with the outer surface of the pinion slider 4 with a lower end of the rubber ring 8b being bent, as shown in FIG. 9.
In such a conventional structure, there is a tendency that water is caught within the bent portion of the rubber ring 8b. Particularly, when such starter motor is mounted on an engine with the pinion thereof being upside, the rubber ring 8b may receive and store water in its valley. Such water in the valley portion of the rubber ring 8b may easily enter into the front frame 1 due to thermal aspiration and/or vibration and may consequently cause the bearing 6 to rust, so that smooth sliding of the pinion slider 4 can not be obtained. Water that has entered into the front frame 1 may easily enter into the d.c. motor causing the latter to be damaged.